ORCID Profile
0000-0002-5227-4631
Current Organisation
Deakin University
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Publisher: AIP Publishing
Date: 06-2021
DOI: 10.1063/5.0055723
Abstract: Period bubbling bifurcation and transition to chaotic state of a convective flow on the top-open cylinder beneath heating are investigated using direct numerical simulation owing to its fundamental significance and extensive application. Numerical results show that a primary convective flow on the cylinder is axisymmetric and dominated by the effect of baroclinicity for small Rayleigh numbers. There exists a complex route of the transition to chaotic state involving a succession of bifurcations when the Rayleigh number is increased that is, the pitchfork bifurcation occurs between Ra = 2.7 × 103 and Ra = 2.8 × 103 for which an axisymmetric convective flow is broken, and the first Hopf bifurcation occurs between Ra = 3.3 × 105 and Ra = 3.4 × 105. An interesting phenomenon is that the convective flow may change from periodic back to steady state with the increase in the Rayleigh number for 7.0 × 105 ≤ Ra ≤ 1.5 × 106, termed as a period bubbling bifurcation. The whole route of the transition to chaotic state can be described by a steady, a periodic, a steady again, a period doubling, a quasiperiodic, and a chaotic state as the Rayleigh number is increased. Further, the convective flow in the transition is discussed by employing the topologic index, the spectral analysis, the attractor, and the fractal dimension. Additionally, heat transfer is also quantified.
Publisher: Cambridge University Press (CUP)
Date: 28-02-2022
DOI: 10.1017/JFM.2022.134
Abstract: Natural convection adjacent to a curved vertical wall is widely present. Unfortunately, the effect of curvature on the transient thermal boundary layer (TBL) adjacent to the concave vertical wall has been neglected. In this study, dynamical evolution and thermal process of transient natural convection in a vertical circular pipe are discussed using scaling analysis, a boundary flow regime for the thin TBL without merging and a duct flow regime for the TBL with merging at the axis of the pipe are distinguished. The scaling laws quantifying the dependence of thickness, velocity and flow rate of the TBL of the fluid with the fixed Prandtl number in the vertical pipe on the Rayleigh number ( Ra T and Ra q ) and the ratio of height to radius of the pipe ( A ) are first reported for the isothermal and isoflux conditions. The curvature effect becomes stronger with the increase of the thickness of the TBL. Under the duct flow regime, the non-dimensional flow rate is scaled with $Ra_T^{1/2}{A^{ - 1}}$ for the isothermal condition and with $Ra_q^{1/2}{A^{ - 3/2}}$ for the isoflux condition. The scaling laws of the thickness, velocity and the flow rate of the TBL in the vertical pipe are validated based on the numerical results from direct numerical simulation (DNS) with good precision. The scaling coefficient is also presented under different regimes and conditions, which can serve as a design guide to determine natural convection in the vertical circular pipe.
Publisher: Elsevier BV
Date: 06-2021
Publisher: Cambridge University Press (CUP)
Date: 25-10-2023
DOI: 10.1017/JFM.2023.632
Publisher: AIP Publishing
Date: 12-2018
DOI: 10.1063/1.5054847
Publisher: AIP Publishing
Date: 09-2022
DOI: 10.1063/5.0103760
Abstract: A transition to the chaotic state of the convective flows on a hot cone is investigated using three-dimensional numerical simulation. A wide range of the Rayleigh number from Ra = 100 to 107 for the Prandtl number of Pr = 7 and the aspect ratio of A = 0.1 is considered. Numerical results reveal a complex transition route to the chaotic state of the convective flows with a succession of Hopf, period-doubling, and quasiperiodic bifurcations the transition to a chaotic state followed by a succession of inverse quasiperiodic and inverse period-doubling bifurcations and a succession of period-doubling and quasiperiodic bifurcations and the transition to chaotic state again. Typical flows in the transition are characterized and analyzed using spectral analysis, the trajectory, the largest Lyapunov exponent, and the fractal dimension. Further, heat transfer in the transition is calculated, and the scaling relation is obtained.
Publisher: AIP Publishing
Date: 02-2019
DOI: 10.1063/1.5083671
Abstract: Natural convection on a convectively heated vertical wall, one of the fundamental issues of heat and mass transfer in many engineering applications, is investigated in this work. The configuration is governed by the Rayleigh number (RaL or Ra), the Prandtl number (Pr), and the non-dimensional convective heat transfer coefficient (CiL or Ci). A scaling analysis for the dynamics of the boundary layer flow and heat transfer is carried out. The scales of the velocity/thickness of the boundary layer flow and the temperature/thickness of the thermal boundary layer related to the non-dimensional governing parameters are obtained. The scales are validated using the numerical results by large eddy simulation. The results show that the non-dimensional velocity of the boundary layer flow is proportional to CiL2/5RaL2/5 the thickness from the wall to the layer of the maximal velocity is inversely proportional CiL1/5RaL1/5 the non-dimensional thickness of the thermal boundary layer is inversely proportional CiL1/5RaL1/5 the non-dimensional temperature in the thermal boundary layer is proportional to CiL4/5RaL−1/5. The reduction factor describing the thermal resistance of the thermal boundary layer is further discussed, which is proportional to Ci4/5Ra−1/5.
Publisher: MDPI AG
Date: 26-09-2018
DOI: 10.3390/NU10101376
Abstract: Despite the abundance of plant-derived fats in our diet, their effects on appetite, and metabolic markers, remain unclear. This single-blinded 3-way cross-over pilot study aimed to investigate the ability of the two most abundant dietary plant-derived fats, oleic (OA) and linoleic (LA) acids, to modulate postprandial appetite and levels of circulating appetite and metabolic regulators in overweight/obese in iduals. Meals were a high-carbohydrate control, a high-OA or a high-LA meal, and provided 30% of participants’ estimated energy requirements. Meals were consumed after an overnight fast, with blood s les collected over 3¼ h. Appetite parameters were assessed via a validated visual analogue scale questionnaire. Hormones and other circulating factors were quantified using multiplex immunoassays. Eight participants (age 45.8 ± 3.6 (years), body mass index 32.0 ± 1.3 (kg/m2)) completed the study. All meals significantly increased fullness and reduced desire to eat. The control and high-OA meals significantly decreased prospective food intake. The high-LA meal increased ghrelin levels (p 0.05), a hormone which encourages food intake. This was coupled with a significant acute increase in resistin levels, which impairs insulin signaling. Taken together, this study indicates that in overweight/obese in iduals, high-LA meals may promote excess energy intake and alter glucose handling, though a larger cohort may be required to strengthen results.
No related grants have been discovered for Bingchuan Nie.